How do they work

The basic loop is simple:
Feed
Burp
Change diaper
Get to sleep
Repeat

Then you need to work in a "change clothes" subroutine, which runs once/day, or when the outfit is filthy.

But while that loop is running, you need to frequently:
Maintain eye contact
Smile
Talk (content not important; babies hear high pitches better)
Play (Peek-a-boo works with a wide range of ages, but basically any repetitive action delivered with a smile will amuse a baby)

And snuggling. Lots and lots of snuggling.